302 MOEPHOLOGY AND EVOLUTION
three trunks as in Man, but that is not always the case. The nerves divide and unite among themselves to form groups of nerves or distinct cords. The arrangement most closely approximates to the human condition in the Orang.
In the Chimpanzee (fig. 55), before the nerves form the plexus the following branches are given off:—
(1) Communicating to the phrenic nerve from
(2) Long thoracic nerve (L.T.N.) from C5, C6,
(3) To first digitation of serratus rnagnus.
(4) To scalenus anticus (Seal. Ant.) from C7 and
The fifth cervical nerve gives off the following branches before it enters the plexus :—
(1) Nerve to the levator anguli scapulae (L.A.S.),
rhomboidei (E.M.) and first digitation of serratus magnus (S.A.M.).
(2) Suprascapular nerve (S-S.N.).
The sixth cervical nerve divides into anterior and posterior divisions. The seventh cervical gives off the external anterior thoracic nerve (E.A.T.) and then divides into anterior and posterior divisions. The eighth cervical and first dorsal nerves unite to form a lower trunk, which gives off the internal anterior thoracic nerve (I.A.T.) and then divides into anterior and posterior divisions. Thus there is no upper trunk as in Man.
The fifth cervical nerve unites with the anterior Divisions of C6 and C7 to form a cord which, after giving off the musculo-cutaneous nerve (M-C.N.) unites with